Re: How to track the functions in self-written module using SystemTap?

[David Smith <dsmith@redhat.com>]

On 12/02/2015 07:13 PM, Nan Xiao wrote:
> Hi David,
> 
> (1)
>>>> Hmm. OK, let's try a couple more things:
>>>
>>>> 1) It could be that systemtap is missing the module load somehow. So,
>>>> try this:
>>>
>>>> - load the module
>>>> - run stap
>>>> - exercise the module
>>>> - unload the module
>>>> - kill stap
>>>
>>> Still outputs nothing.
> 
>> Can you do the same thing here and add '-DDEBUG_KPROBES' to the stap
>> command and show us the output?
> 
> After adding '-DDEBUG_KPROBES', the stap command still outputs nothing.

Hmm.

> (2)
> [root@localhost testsuite]# make installcheck
> RUNTESTFLAGS="modules_out_of_tree.exp kmodule.exp"
> 
> 
> Running ./systemtap.base/kmodule.exp ...
> 
>                 === systemtap Summary ===
> 
> # of expected passes            7

Ah. It ran kmodule.exp, but not modules_out_of_tree.exp. You are running
systemtap 2.4, and that testcase was first present in systemtap 2.6.

I was testing another bug so I had a RHEL 7.0 systemtap set up and I
installed systemtap 2.4 on it. It looks like that version can't probe
out-of-tree modules.

It looks like you've got a couple of options:

1) Copy your module into the kernel module tree (located at
/lib/modules/`uname -r`/kernel) to use systemtap on it.

2) Upgrade systemtap to at least 2.6. (I ran systemtap 2.6 on a RHEL 7.1
system, and the modules_out_of_tree.exp test case passed there.)

-- 
David Smith
dsmith@redhat.com
Red Hat
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